Desmozoon lepeophtheriin. gen., n. sp., (Microsporidia: Enterocytozoonidae) infecting the salmon louse Lepeophtheirus salmonis(Copepoda: Caligidae)

Freeman, Sommerville, Sommerville Christina

Description

A microsporidian was previously reported to infect the crustacean parasite, Lepeophtheirus salmonis (Krøyer, 1837) (Copepoda, Caligidae), on farmed Atlantic salmon ( Salmo salar L.) in Scotland. The microsporidian was shown to be a novel species with a molecular phylogenetic relationship to Nucleospora (Enterocytozoonidae), but the original report did not assign it to a genus or species. Further studies examined the development of the microsporidian in L. salmonis using electron microscopy and re-evaluated the molecular findings using new sequence data available for the group. Here we report a full description for the microsporidian and assign it to a new genus and species. Results The microsporidian infects subcuticular cells that lie on the innermost region of the epidermal tissue layer beneath the cuticle and along the internal haemocoelic divisions. The mature spores are sub-spherical with a single nucleus and an isofilar polar filament with 5-8 turns in a double coil. The entire development is in direct contact with the host cell cytoplasm and is polysporous. During early merogony, a diplokaryotic nuclear arrangement exists which is absent throughout the rest of the developmental cycle. Large merogonial plasmodia form which divide to form single uninucleate sporonts. Sporogonial plasmodia were not observed; instead, binucleate sporonts divide to form two sporoblasts. Prior to final division, there is a precocious development of the polar filament extrusion apparatus which is associated with large electron lucent inclusions (ELIs). Analyses of DNA sequences reveal that the microsporidian is robustly supported in a clade with other members of the Enterocytozoonidae and confirms a close phylogenetic relationship with Nucleospora . Conclusion The ultrastructural findings of the precocious development of the polar filament and the presence of ELIs are consistent with those of the Enterocytozoonidae. However, the confirmed presence of an early diplokaryotic stage and a merogonial plasmodium that divides to yield uninucleate sporonts instead of transforming into a sporogonial syncitium, are features not currently associated with the family. Yet, analyses of DNA sequence data clearly place the microsporidian within the Enterocytozoonidae. Therefore, due to the novelty of the copepod host, the ultrastructural findings and the robust nature of the phylogenetic analyses, a new genus should be created within the Enterocytozoonide; Desmozoon lepeophtherii n. gen. n. sp. is proposed.

Informations

• Publié par: biomed
• Publié le: 01 janvier 2009
• Nombre de lectures: 48
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Pga e 1fo1  ( 5 apegum nr bet nor foaticnoitrup esops)

Bio Med Central

Research Open Access Desmozoon lepeophtherii n. gen., n. sp., (Microsporidia: Enterocytozoonidae) infecting the salmon louse Lepeophtheirus salmonis (Copepoda: Caligidae) Mark A Freeman* †1,2 and Christina Sommerville †1

Address: 1 Institute of Aquaculture, University of Stirling, Stirling, FK9 4LA, UK and 2 Institute of Earth and Ocean Sciences, University of Malaya, Kuala Lumpur, 50603, Malaysia Email: Mark A Freeman* - [e-mail]; Christina Sommerville - [e-mail] * Corresponding author †Equal contributors

Parasites & Vectors

Published: 27 November 2009 Received: 1 November 2009 Parasites & Vectors 2009, 2 :58 doi:10.1186/1756-3305-2-58  Accepted: 27 November 2009 This article is available from: http:// www.parasitesandvectors.com/content/2/1/58 © 2009 Freeman and Sommerville; li censee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons. org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the orig inal work is properly cited.

Abstract Background: A microsporidian was previously report ed to infect the crustacean parasite, Lepeophtheirus salmonis (Krøyer, 1837) (Copepoda, Caligidae), on farmed Atlantic salmon ( Salmo salar L.) in Scotland. The microsporidian was shown to be a novel species with a molecular phylogenetic relationship to Nucleospora (Enterocytozoonidae), but th e original report did not assign it to a genus or species. Further studies examined the development of the microsporidian in L. salmonis using electron microscopy and re-evaluated the molecular findings using new sequence data available for the group. Here we report a fu ll description for the microsporidian and assign it to a new genus and species. Results: The microsporidian infects subcuticular cell s that lie on the innermost region of the epidermal tissue layer beneath th e cuticle and along the internal haemocoelic divisions. The mature spores are sub-spherical with a si ngle nucleus and an isofilar pola r filament with 5-8 turns in a double coil. The entire development is in di rect contact with the host cell cytoplasm and is polysporous. During early merogony, a diplokaryo tic nuclear arrangement exists which is absent throughout the rest of the deve lopmental cycle. Large merogonial plasmodia form which divide to form single uninucleate sporonts. Sporogonial pl asmodia were not observed; instead, binucleate sporonts divide to form two spor oblasts. Prior to final division, there is a precocious development of the polar filament extrusion apparatus which is associated with large electron lucent inclusions (ELIs). Analyses of DNA sequences reveal that the microsporidian is robustly supported in a clade with other members of the Ente rocytozoonidae and confirms a close phylogenetic relationship with Nucleospora . Conclusion: The ultrastructural findings of the precocio us development of the polar filament and the presence of ELIs are consis tent with those of the Enterocyto zoonidae. However, the confirmed presence of an early diplokaryo tic stage and a merogonial plas modium that divides to yield uninucleate sporonts instead of transforming in to a sporogonial syncitium, are features not currently associated with the family. Yet, an alyses of DNA sequence data clearly place the microsporidian within the Entero cytozoonidae. Therefore, due to th e novelty of the copepod host, the ultrastructural findings and the robust nature of the phylogenetic anal yses, a new genus should be created within the Enterocytozoonide; Desmozoon lepeophtherii n. gen. n. sp. is proposed.